diff --git a/.github/CODEOWNERS b/.github/CODEOWNERS
index 0a8cb5e5..6b0f08df 100644
--- a/.github/CODEOWNERS
+++ b/.github/CODEOWNERS
@@ -34,6 +34,9 @@
 
 /modules/misc/xdg-user-dirs.nix                       @pacien
 
+/modules/misc/xdg-system-dirs.nix                     @tadfisher
+/tests/modules/misc/xdg/system-dirs.nix               @tadfisher
+
 /modules/programs/aria2.nix                           @JustinLovinger
 
 /modules/programs/autojump.nix                        @evanjs
diff --git a/modules/misc/news.nix b/modules/misc/news.nix
index 6234dc7b..daa86665 100644
--- a/modules/misc/news.nix
+++ b/modules/misc/news.nix
@@ -1965,7 +1965,7 @@ in
           The option 'services.sxhkd.extraPath' has been deprecated.
         '';
       }
-      
+
       {
         time = "2021-05-06T20:47:37+00:00";
         condition = hostPlatform.isLinux;
@@ -1980,6 +1980,26 @@ in
           A new module is available: 'programs.nix-index'.
         '';
       }
+
+      {
+        time = "2021-05-10T18:50:07+00:00";
+        message = ''
+          A new module is available: 'xdg.systemDirs'. Options are:
+
+          - xdg.systemDirs.config
+
+            Extra directory names to add to $XDG_CONFIG_DIRS in the user
+            session.
+
+          - xdg.systemDirs.data
+
+            Extra directory names to add to $XDG_DATA_DIRS in the user
+            session.
+
+          These variables are visible in both systemd user services and
+          login shells.
+        '';
+      }
     ];
   };
 }
diff --git a/modules/misc/xdg-system-dirs.nix b/modules/misc/xdg-system-dirs.nix
new file mode 100644
index 00000000..d3fad015
--- /dev/null
+++ b/modules/misc/xdg-system-dirs.nix
@@ -0,0 +1,49 @@
+{ config, lib, pkgs, ... }:
+
+with lib;
+
+let
+
+  cfg = config.xdg.systemDirs;
+
+  configDirs = concatStringsSep ":" cfg.config;
+
+  dataDirs = concatStringsSep ":" cfg.data;
+
+in {
+  meta.maintainers = with maintainers; [ tadfisher ];
+
+  options.xdg.systemDirs = {
+    config = mkOption {
+      type = types.listOf types.str;
+      default = [ ];
+      example = literalExample ''[ "/etc/xdg" ]'';
+      description = ''
+        Directory names to add to <envar>XDG_CONFIG_DIRS</envar>
+        in the user session.
+      '';
+    };
+
+    data = mkOption {
+      type = types.listOf types.str;
+      default = [ ];
+      example = literalExample ''[ "/usr/share" "/usr/local/share" ]'';
+      description = ''
+        Directory names to add to <envar>XDG_DATA_DIRS</envar>
+        in the user session.
+      '';
+    };
+  };
+
+  config = mkMerge [
+    (mkIf (cfg.config != [ ]) {
+      systemd.user.sessionVariables.XDG_CONFIG_DIRS =
+        "${configDirs}\${XDG_CONFIG_DIRS:+:$XDG_CONFIG_DIRS}";
+    })
+
+    (mkIf (cfg.data != [ ]) {
+      systemd.user.sessionVariables.XDG_DATA_DIRS =
+        "${dataDirs}\${XDG_DATA_DIRS:+:$XDG_DATA_DIRS}";
+    })
+  ];
+}
diff --git a/modules/modules.nix b/modules/modules.nix
index 6a6f4f08..573764b3 100644
--- a/modules/modules.nix
+++ b/modules/modules.nix
@@ -40,6 +40,7 @@ let
     (loadModule ./misc/tmpfiles.nix { condition = hostPlatform.isLinux; })
     (loadModule ./misc/version.nix { })
     (loadModule ./misc/vte.nix { })
+    (loadModule ./misc/xdg-system-dirs.nix { condition = hostPlatform.isLinux; })
     (loadModule ./misc/xdg-mime.nix { condition = hostPlatform.isLinux; })
     (loadModule ./misc/xdg-mime-apps.nix { condition = hostPlatform.isLinux; })
     (loadModule ./misc/xdg-user-dirs.nix { condition = hostPlatform.isLinux; })
diff --git a/modules/systemd.nix b/modules/systemd.nix
index e1261b7b..7c03b562 100644
--- a/modules/systemd.nix
+++ b/modules/systemd.nix
@@ -333,6 +333,11 @@ in
             unset systemdStatus
           ''
       );
+
+      # Export environment variables in systemd.user.sessionVariables to login shells.
+      home.sessionVariablesExtra = optionalString (cfg.sessionVariables != {}) ''
+        export $(${pkgs.systemd}/lib/systemd/user-environment-generators/30-systemd-environment-d-generator)
+      '';
     })
   ];
 }
diff --git a/modules/targets/generic-linux.nix b/modules/targets/generic-linux.nix
index a6486d73..6e17bd28 100644
--- a/modules/targets/generic-linux.nix
+++ b/modules/targets/generic-linux.nix
@@ -4,9 +4,19 @@ with lib;
 
 let
 
+  cfg = config.targets.genericLinux;
+
   profileDirectory = config.home.profileDirectory;
 
 in {
+  imports = [
+    (mkRenamedOptionModule [ "targets" "genericLinux" "extraXdgDataDirs" ] [
+      "xdg"
+      "systemDirs"
+      "data"
+    ])
+  ];
+
   options.targets.genericLinux = {
     enable = mkEnableOption "" // {
       description = ''
@@ -14,39 +24,20 @@ in {
         GNU/Linux distributions other than NixOS.
       '';
     };
-
-    extraXdgDataDirs = mkOption {
-      type = types.listOf types.str;
-      default = [ ];
-      example = [ "/usr/share" "/usr/local/share" ];
-      description = ''
-        List of directory names to add to <envar>XDG_DATA_DIRS</envar>.
-      '';
-    };
   };
 
-  config = mkIf config.targets.genericLinux.enable {
-    home.sessionVariables = let
-      profiles =
-        [ "\${NIX_STATE_DIR:-/nix/var/nix}/profiles/default" profileDirectory ];
-      dataDirs = concatStringsSep ":"
-        (map (profile: "${profile}/share") profiles
-          ++ config.targets.genericLinux.extraXdgDataDirs);
+  config = mkIf cfg.enable {
+    xdg.systemDirs.data = [
+      # Nix profiles
+      "\${NIX_STATE_DIR:-/nix/var/nix}/profiles/default/share"
+      "${profileDirectory}/share"
 
-      # https://github.com/archlinux/svntogit-packages/blob/packages/ncurses/trunk/PKGBUILD
-      # https://salsa.debian.org/debian/ncurses/-/blob/master/debian/rules
-      # https://src.fedoraproject.org/rpms/ncurses/blob/main/f/ncurses.spec
-      # https://gitweb.gentoo.org/repo/gentoo.git/tree/sys-libs/ncurses/ncurses-6.2-r1.ebuild
-      distroTerminfoDirs = concatStringsSep ":" [
-        "/etc/terminfo" # debian, fedora, gentoo
-        "/lib/terminfo" # debian
-        "/usr/share/terminfo" # package default, all distros
-      ];
-    in {
-      XDG_DATA_DIRS = "${dataDirs}\${XDG_DATA_DIRS:+:}$XDG_DATA_DIRS";
-      TERMINFO_DIRS =
-        "${profileDirectory}/share/terminfo:$TERMINFO_DIRS\${TERMINFO_DIRS:+:}${distroTerminfoDirs}";
-    };
+      # Distribution-specific
+      "/usr/share/ubuntu"
+      "/usr/local/share"
+      "/usr/share"
+      "/var/lib/snapd/desktop"
+    ];
 
     home.sessionVariablesExtra = ''
       . "${pkgs.nix}/etc/profile.d/nix.sh"
@@ -62,8 +53,20 @@ in {
       . "${profileDirectory}/etc/profile.d/hm-session-vars.sh"
     '';
 
-    systemd.user.sessionVariables = {
+    systemd.user.sessionVariables = let
+      # https://github.com/archlinux/svntogit-packages/blob/packages/ncurses/trunk/PKGBUILD
+      # https://salsa.debian.org/debian/ncurses/-/blob/master/debian/rules
+      # https://src.fedoraproject.org/rpms/ncurses/blob/main/f/ncurses.spec
+      # https://gitweb.gentoo.org/repo/gentoo.git/tree/sys-libs/ncurses/ncurses-6.2-r1.ebuild
+      distroTerminfoDirs = concatStringsSep ":" [
+        "/etc/terminfo" # debian, fedora, gentoo
+        "/lib/terminfo" # debian
+        "/usr/share/terminfo" # package default, all distros
+      ];
+    in {
       NIX_PATH = "$HOME/.nix-defexpr/channels\${NIX_PATH:+:}$NIX_PATH";
+      TERMINFO_DIRS =
+        "${profileDirectory}/share/terminfo:$TERMINFO_DIRS\${TERMINFO_DIRS:+:}${distroTerminfoDirs}";
     };
   };
 }
diff --git a/tests/modules/home-environment/session-variables.nix b/tests/modules/home-environment/session-variables.nix
index d939c05e..5f52b620 100644
--- a/tests/modules/home-environment/session-variables.nix
+++ b/tests/modules/home-environment/session-variables.nix
@@ -15,6 +15,7 @@ let
     export XDG_CACHE_HOME="/home/hm-user/.cache"
     export XDG_CONFIG_HOME="/home/hm-user/.config"
     export XDG_DATA_HOME="/home/hm-user/.local/share"
+    export $(${pkgs.systemd}/lib/systemd/user-environment-generators/30-systemd-environment-d-generator)
   '';
 
   darwinExpected = ''
diff --git a/tests/modules/misc/xdg/default.nix b/tests/modules/misc/xdg/default.nix
index 813a2520..45610154 100644
--- a/tests/modules/misc/xdg/default.nix
+++ b/tests/modules/misc/xdg/default.nix
@@ -1,4 +1,5 @@
 {
   xdg-mime-apps-basics = ./mime-apps-basics.nix;
   xdg-file-attr-names = ./file-attr-names.nix;
+  xdg-system-dirs = ./system-dirs.nix;
 }
diff --git a/tests/modules/misc/xdg/system-dirs.nix b/tests/modules/misc/xdg/system-dirs.nix
new file mode 100644
index 00000000..d2913b23
--- /dev/null
+++ b/tests/modules/misc/xdg/system-dirs.nix
@@ -0,0 +1,25 @@
+{ config, lib, pkgs, ... }:
+
+{
+  config = {
+    xdg.systemDirs.config = [ "/etc/xdg" "/foo/bar" ];
+    xdg.systemDirs.data = [ "/usr/local/share" "/usr/share" "/baz/quux" ];
+
+    nmt.script = ''
+      envFile=home-files/.config/environment.d/10-home-manager.conf
+      assertFileExists $envFile
+      assertFileContent $envFile ${
+        pkgs.writeText "expected" ''
+          LOCALE_ARCHIVE_2_27=${pkgs.glibcLocales}/lib/locale/locale-archive
+          XDG_CONFIG_DIRS=/etc/xdg:/foo/bar''${XDG_CONFIG_DIRS:+:$XDG_CONFIG_DIRS}
+          XDG_DATA_DIRS=/usr/local/share:/usr/share:/baz/quux''${XDG_DATA_DIRS:+:$XDG_DATA_DIRS}
+        ''
+      }
+
+      sessionVarsFile=home-path/etc/profile.d/hm-session-vars.sh
+      assertFileExists $sessionVarsFile
+      assertFileContains $sessionVarsFile \
+        'export $(${pkgs.systemd}/lib/systemd/user-environment-generators/30-systemd-environment-d-generator)'
+    '';
+  };
+}
diff --git a/tests/modules/systemd/session-variables.nix b/tests/modules/systemd/session-variables.nix
index 59d1a4d3..21d96d44 100644
--- a/tests/modules/systemd/session-variables.nix
+++ b/tests/modules/systemd/session-variables.nix
@@ -15,6 +15,11 @@
         V_int=1
         V_str=2
       ''}
+
+      sessionVarsFile=home-path/etc/profile.d/hm-session-vars.sh
+      assertFileExists $sessionVarsFile
+      assertFileContains $sessionVarsFile \
+        'export $(${pkgs.systemd}/lib/systemd/user-environment-generators/30-systemd-environment-d-generator)'
     '';
   };
 }
diff --git a/tests/modules/targets-linux/generic-linux.nix b/tests/modules/targets-linux/generic-linux.nix
index 530137cf..88cec8a0 100644
--- a/tests/modules/targets-linux/generic-linux.nix
+++ b/tests/modules/targets-linux/generic-linux.nix
@@ -2,26 +2,36 @@
 
 with lib;
 
-{
+let
+  expectedXdgDataDirs = concatStringsSep ":" [
+    "\${NIX_STATE_DIR:-/nix/var/nix}/profiles/default/share"
+    "/home/hm-user/.nix-profile/share"
+    "/usr/share/ubuntu"
+    "/usr/local/share"
+    "/usr/share"
+    "/var/lib/snapd/desktop"
+    "/foo"
+  ];
+
+in {
   config = {
-    targets.genericLinux = {
-      enable = true;
-      extraXdgDataDirs = [ "/foo" ];
-    };
+    targets.genericLinux.enable = true;
+
+    xdg.systemDirs.data = [ "/foo" ];
 
     nmt.script = ''
-      assertFileExists home-path/etc/profile.d/hm-session-vars.sh
+      envFile=home-files/.config/environment.d/10-home-manager.conf
+      assertFileExists $envFile
+      assertFileContains $envFile \
+        'XDG_DATA_DIRS=${expectedXdgDataDirs}''${XDG_DATA_DIRS:+:$XDG_DATA_DIRS}'
+      assertFileContains $envFile \
+        'TERMINFO_DIRS=/home/hm-user/.nix-profile/share/terminfo:$TERMINFO_DIRS''${TERMINFO_DIRS:+:}/etc/terminfo:/lib/terminfo:/usr/share/terminfo'
 
-      assertFileContains \
-        home-path/etc/profile.d/hm-session-vars.sh \
-        'export XDG_DATA_DIRS="''${NIX_STATE_DIR:-/nix/var/nix}/profiles/default/share:/home/hm-user/.nix-profile/share:/foo''${XDG_DATA_DIRS:+:}$XDG_DATA_DIRS"'
-      assertFileContains \
-        home-path/etc/profile.d/hm-session-vars.sh \
+      sessionVarsFile=home-path/etc/profile.d/hm-session-vars.sh
+      assertFileExists $sessionVarsFile
+      assertFileContains $sessionVarsFile \
         '. "${pkgs.nix}/etc/profile.d/nix.sh"'
 
-      assertFileContains \
-        home-path/etc/profile.d/hm-session-vars.sh \
-        'export TERMINFO_DIRS="/home/hm-user/.nix-profile/share/terminfo:$TERMINFO_DIRS''${TERMINFO_DIRS:+:}/etc/terminfo:/lib/terminfo:/usr/share/terminfo"'
       assertFileContains \
         home-path/etc/profile.d/hm-session-vars.sh \
         'export TERM="$TERM"'